Why does the Ground Fault Protection (GFP) fuse keep blowing in my Grid Tie inverter?
Understanding Ground Faults
The ground fault protection (GFP) fuse is blowing due to excess current flowing between ground and the grounded terminal of the PV array. The two most common types of ground faults are negative and positive ground faults.
Negative Ground Fault
A negative ground fault is the most common type of ground fault. This type of ground fault occurs when there is a voltage difference between ground and the terminal of the PV array that is supposed to be bonded to ground. As the inverter increases in power, the amount of current flowing through the ground conductor increases, eventually blowing the GFP fuse.
Figure 1: A negatively grounded PV array with a short between the negative terminal of the array and the ground path.
Positive Ground Fault
A positive ground fault is rare, but can occur, usually when not following proper wire bend radius rules. This type of ground fault occurs when the ungrounded terminal of the PV array has a low resistance connection to ground. This type of ground fault can cause the GFP fuse to blow even while the inverter is powered off or while the ungrounded terminal is disconnected. It is recommended to be extremely careful with this type of ground fault and the grounded terminal of the PV array should be disconnected until the source of the low resistance path can be found.
Figure 2: A negatively grounded PV array with a short between the positive terminal of the array and the grounded chassis of the array.